1. Field of the Invention
The present invention relates to an indicating system for determining at least one engine parameter which includes a sensor unit that records a measured variable having a component that is dependent on the crank angle, and a computing unit that is connected to the sensor unit via an input, and further relates to an associated method for determining a parameter, and use in engine control.
2. The Prior Art
A complex sensor system and indicating technique may be used on engine test benches to obtain any desired engine parameter—understood to mean characteristic values and parameters of the internal combustion engine (diesel or spark ignition engine, for example) to be tested, or the operating characteristics thereof (during an operating cycle, for example)—or to compute same from measured values. The indicating system also generally includes a signal amplifier which appropriately processes, for example amplifies, conditions, filters, and/or digitizes, a sensor signal for further use. For certain sensors, such as the piezoelectric cylinder pressure sensors which are particularly important for the indicating technique, a charge amplifier is generally used as a signal amplifier. However, it is also possible to use, for example, strain gauges, piezoresistive pressure sensors, structure-borne noise sensors, sensors for sonic and ultrasonic emission analysis, ion current probes, flame radiation sensors, sensors for needle, valve, or piston lift, etc., each of which uses associated signal amplifiers. The necessary engine parameters are then often computed from the measured variables such as cylinder pressure, crank angle, etc., in separate downstream processing units, or measured variables such as cylinder pressure are evaluated on a time basis or on the basis of the measured crank angle for determining the engine parameters, whereby the computations and evaluations may also be performed online, i.e., during engine operation, or offline, i.e., after the fact. As a result, the processing units require their own input for a crank angle signal, for example from an angle sensor. Nevertheless, some internal parameters may also be determined without the crank angle information. For example, on the basis of the measured variation in the cylinder pressure over time, parameters such as peak pressure, combustion noise, knock intensity, frequency components, time differences between significant signal characteristics, etc., may also be determined without crank angle information. However, for their determination, even if only as an approximation, other important parameters such as the indicated average pressure, mass conversion points, course of combustion, combustion center of gravity, components of order analysis, ignition delay in degrees of the crank angle, etc., absolutely require, in addition to the cylinder pressure, crank angle information such as rotational speed, duration of one revolution of the crankshaft, instantaneous angular velocity, duration of an operating cycle, duration of an operating cycle divided by the number of cylinders, or an instantaneous rotational angle in any given angular resolution. Measurement of the crank angle information naturally increases the complexity of the sensor system. On engine test benches this complexity is often justified, since as a rule the most accurate determination possible of certain parameters and the most precise evaluation possible of the engine operation is desired, although for cost reasons the level of complexity is frequently minimized for this application. Another problem, of course, is the space requirement for a complex sensor system and indicating technique, and the fact that the necessary sensors can usually be retrofitted on the engine only with a great level of effort.
In principle, of course, it is also known to use an essentially periodic measurement signal, for example from a cylinder pressure sensor, to derive crank angle information. AT 388 830 B, for example, discloses that the drift compensation device of a charge amplifier circuit is triggered corresponding to the period of a measurement signal. The periodic trigger signals for the triggering device (i.e., essentially crank angle information) may be related to a crankshaft, either internally on the basis of the measurement signal, or externally on the basis of a connected signal transmitter.
The article “Simulationsmodelle von Verbrennungsmotoren für Echtzeitan-wendungen” [Simulation models for real-time applications in internal combustion engines], Gheorghiu V., Haus der Technik e.V., Session No. E-30-202-056-8, 1998 describes a method for computing crank angle information from the variation of pressure measured over time, also taking into account irregularities in the crankshaft revolutions.
Of course, these methods for determining crank angle information from an essentially periodic measurement signal provide only approximations of the required crank angle information. The resulting error depends essentially on the methods used for determining the crank angle information. For applications in the area of engine test benches, such approximation methods are generally unsuitable and therefore have not been considered. However, for use in the area of vehicle onboard measurement or indicating techniques or in the low-end indicating market, such indicating techniques are too costly and complicated.
Charge amplifiers having integrated peak value determination on the basis of the measurement signal are currently known. Such charge amplifiers have limited usefulness, however, since they allow only a single engine parameter to be determined and provide no flexibility. However, various engine parameters are generally required for meaningful use.
The object of the present invention is to provide an indicating arrangement which has a particularly simple and compact design, is advantageous, easy to install and operate, and still allows important engine parameters to be determined, and an associated method.